Live Previewer

Live Previewer is the closest thing in the lhyNodes pack to a vanity node: it does nothing to your data, computes nothing, and yet people drop it in when a long Wan or video render makes them want the picture right there on the canvas instead of in a corner of the browser.

It's a display-only node. Drag it onto the graph and you get a resizable ~300×300 window that fills with the live preview frame during a run. That's the whole job. On the backend it's a no-op - the Python class is literally a do_nothing() that returns an empty tuple and is flagged as an output node so the engine doesn't get confused by a node with zero sockets. The real work happens in the pack's frontend extension, which listens for the server's b_preview websocket event and paints the incoming blob into the node's canvas, updating the title with the step counter (23/30, that kind of thing) as it goes.

So the honest summary: it's a monitor, not a switch. If your setup emits live previews over the websocket, this is a nice way to keep an eye on a long render without hunting for the tiny preview strip. If nothing upstream emits b_preview, the node just sits there empty - which trips people up the first time. It is not a generic image viewer. If you want to look at a finished tensor, use the normal Preview Image node, not this.

Where it shines is the middle of a busy graph. You've got a 30-frame video render that's going to take ten minutes; the preview window is at the other end of the tab and you want to catch a garbage frame early so you can interrupt. Plop a Live Previewer anywhere visible, and during the run it shows you exactly what the sampler is doing. It also pairs conceptually with the same pack's DynamicParameterPanel, which has a live_preview toggle for the same kind of streaming preview - same idea, different host.

Installing it

Live Previewer ships in the lhaoyun6/ComfyUI-lhyNodes pack, an efficiency-node suite from lhaoyun6 (the author behind the popular ComfyUI-FlashVSR_Ultra_Fast video upscaler). Install via ComfyUI Manager by searching for lhyNodes, or by hand:

cd ComfyUI/custom_nodes
git clone https://github.com/lihaoyun6/ComfyUI-lhyNodes.git
python -m pip install -r ComfyUI-lhyNodes/requirements.txt

Restart ComfyUI after. The pack's requirements (ultralytics, opencv-python, numpy, yarl) are shared across all its nodes; this one needs no models or extra downloads.

Gotchas

• No broadcast, no picture. It only renders what the server pushes as b_preview. If your preview settings are off, or the node emitting previews isn't present, the canvas stays blank. That's expected, not a bug.
• It has no inputs and no outputs. You can't wire anything through it, so don't build a graph where it's supposed to gate execution. It's a decoration with a purpose, not a routing node.

It's a niche pick, but for "watch the render from the middle of a big graph" it's the one I'd reach for - zero setup, zero VRAM cost, and it makes a long run feel less like watching paint dry.